Abstract

We demonstrate optical performance monitoring of in-band optical signal to noise ratio (OSNR) and residual dispersion, at bit rates of 40Gb/s, 160Gb/s and 640Gb/s, using slow-light enhanced optical third harmonic generation (THG) in a compact (80µm) dispersion engineered 2D silicon photonic crystal waveguide. We show that there is no intrinsic degradation in the enhancement of the signal processing at 640Gb/s relative to that at 40Gb/s, and that this device should operate well above 1Tb/s. This work represents a record 16-fold increase in processing speed for a silicon device, and opens the door for slow light to play a key role in ultra-high bandwidth telecommunications systems.

Figures (7)

Principle of operation of OPM based on THG. Two signals with the same average power but a different eye diagram quality are converted by the device nonlinear power transfer curve into a bright or faint green light for the undistorted and noisy signal, respectively.

Group index versus wavelength for the silicon engineered PhC waveguide used in this work, having a group index ng~38, nearly constant ( ± 10%) over a wide (~12nm) spectral region. Also shown is the optical spectrum of the 640Gb/s PRBS data stream used in the experiments, showing that the slow light bandwidth is wide enough to accommodate the data bandwidth. Inset: eye diagram of 640Gb/s 33% RZ PRBS modulated signal, as measured with an all-optical sampling oscilloscope.

Experimental setup used to measure both THG as well as perform OPM using THG of a 640GBit/s data signal. For the 40 and 160GBit/s signals, the 8nm filters are replaced with 5nm filters, and launch power varied into the compression set up. Inset: Optically sampled eye diagram of 640GBit/s data signal.

Average THG power versus near-infrared coupled peak power for “clean” (non-degraded) signals at bit rates of 40Gbit/s, 160Gbit/s and 640Gbit/s along with cubic fits to the data. Left: a). The signal for all measurements was tuned to within the slow light region, except black square data which were taken at 640Gbit/s tuned to outside of the SL regime (1542nm). Right b). The normalized curves shown here for 40 and 160Gbit/s were obtained by scaling the raw data by the ratio of signal duty cycle to 640Gbit/s duty cycle (i.e. 4%/33% scaling for 40Gbit/s, 14%/33% scaling for 160Gbit/s).

OSNR monitoring: Relative (normalised to the high OSNR value) THG average power versus input OSNR for fixed coupled power (from top to bottom) at 40Gb/s (top), 160Gb/s (middle) and 640Gb/s (bottom), respectively. Solid lines indicate theoretical curves associated with the three duty cycles used in the experiments. The bottom graph also contains experimental and theoretical results for 40Gbs at 33% duty cycle.